how long before you were comfortable?

How long was it before you guys were conditioned to fight for a full 3 rounds? I'm new so i get side stitches like crazy when i try running, it's hard to keep up with the other guys, i hate doing it but i am forced to walk on the run back to the gym because i'm physically unable to run back.

I'm still getting used to skipping rope, i can just get through 3x3 rounds, my legs are ON fire by the end of it, but that's not hard on my breathing like the running is. Should I just push through the side stitch as long as i can everytime it comes up and will it eventually stop? I try to control my breathing best i can, Big inhales and deep exhales.